Today, in many electronic devices, such as portable communication devices, touch panel displays (touch screens) present information to a user and also receive input from the user. A touch screen is especially useful in portable communication devices where other input devices, such as a keyboard and a mouse, are not easily available.
There are many different types of touch sensing technologies in use today, including capacitive, resistive, infrared, and surface acoustic wave. These technologies sense the position of touches on a screen. However, they do not respond to the pressure that is applied against the touch screen.
For example, it has been proposed in U.S. Pat. No. 6,492,979 to Kent et al. to use a combination of capacitive touch screen and force sensors to prevent false touch. This approach, however, can complicate the sensor interfaces and does not lend itself to sensing different touch forces at the same time. U.S. Pat. No. 7,196,694 to Roberts proposes using force sensors at the peripherals of the touch screen to determine the position of a touch. This however does not offer a capability of multi-touch. It has also been proposed in US Patent Publication No. 2007/0229464 to use a capacitive force sensor array, overlaying a display to form a touch screen. Although this approach offers multi-touch capability, a capacitive pressure sensor has limited spatial resolution and is subject to environmental interferences such as electromagnetic interference (EMI) and capacitive coupling of fingers and other input devices.
Accordingly, there is a need for improved touch sensing technologies and devices.